1. Field of the Invention
The present patent application for industrial invention relates to a public works vehicle provided with a counterweight lifting system, in particular to a drilling machine or boring machine.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
In several countries, and especially in the US, the transportation of public works vehicles, such as for instance drilling machines and excavators, is limited according to their weight. Very strict legislation applies to exceptionally large vehicles. In compliance with said strict regulations, a permission must be obtained in order to circulate with such a heavy load like a public works vehicle. The permissions are expensive and must be applied for much in advance. All of the above requires an economic investment and a planning in terms of movements of the public works vehicles, which are not always possible.
In order to reduce the weight of public works vehicles for transportation purposes, some parts of the public works vehicle are usually dismounted. As it is known, many public works vehicles, such as drilling machines and excavators, are provided with a counterweight that prevents the risk of overturning. Since the counterweight is one of the heaviest parts of the vehicle, the counterweight is generally dismounted in such public works vehicles.
Large-sized excavators (with weight higher than 60 tons) provided with counterweight mounting systems, which simplify the mounting and the dismounting operations of the counterweight, are currently known. Said counterweight mounting systems are mounted on the excavator directly by the vehicle manufacturers.
It must be considered that special machines, such as drilling machines, use the base of an excavator as a base. However, since the mobility of drilling machines is reduced compared to excavators, large-sized drilling machines (with weight higher than 60 tons) can advantageously use the base of smaller excavators, i.e. bases that are designed for excavators with weight lower than 60 tons.
Obviously, the bases of the excavators with weight lower than 60 tons are not provided with any counterweight mounting system. Therefore, especially in the case of drilling machines with weight higher than 60 tons, the problem of safely dismounting and mounting the counterweight arises.
A counterweight can be currently connected to an excavator in basically two different ways.
FIGS. 1 and 2 show an excavator (100) of the prior art. The excavator (100) has a base (2) supported on moving means (3), such as tracks. The base (2) is intended to house one or more engines of the vehicle. The base (2) has a frame (20) and a wall or back plate (21) fixed to the frame (20). Fastenings (22) intended to anchor a counterweight (not shown in FIGS. 1 and 2) protrude in rearward position from the back wall (21). The fastenings (22) can be fixed or revolvingly mounted in the back wall (21) of the base.
With reference to FIG. 3, a counterweight (4) is positioned on the fastenings (22) and fixing screws (40) are passed through the holes (41) of the counterweight (4) and screwed into threaded holes provided in the back wall (21), in such a way to tighten the counterweight (4) and bring it in contact with the back wall (21) of the base.
FIG. 4 shows a variant, in which brackets or shelves (122) are provided instead of the fastenings (22), and welded to the frame (20) of the base of the vehicle. The brackets (122) protrude in rearward position from the frame (20) of the base of the vehicle. The counterweight is positioned on the brackets (122) and screws are inserted from down upwards into through holes of the brackets (122) and screwed to the counterweight, in such manner to firmly connect the counterweight to the brackets (122).
In such a case, the mounting and dismounting operations of the counterweight are dangerous because the operator must work under the brackets (122) and therefore under the counterweight.
In order to mount the counterweight, after lifting the counterweight with a lift, the counterweight must be moved closer to the brackets (122). Now the holes of the brackets must be centered with the holes of the counterweight and then the counterweight must be completely lowered. The centering operation must be made by an operator who needs to place himself under the brackets (122) and by an assistant in charge of moving the counterweight while lifted. Evidently, such a centering operation is very dangerous.
Also the dismounting operation of the counterweight is dangerous because the operator must place himself under the brackets (122) in order to loosen the screws.
Today excavator manufacturers do not provide counterweight lifting systems for medium-sized excavators (with weight lower than 60 tons) because the mounting or dismounting operation of the counterweight is very seldom carried out in this type of excavators.
Large-sized excavators (with weight of 60-90 tons) are provided with counterweight lifting systems, without using any additional counterweight lifting machines that are separated from the vehicle, such as for example cranes.
Two types of counterweight lifting systems are currently known on the market, which differ in the type of counterweight fastening.
FIGS. 5 and 6 show a first counterweight lifting system, which is generally indicated with reference numeral 105. Such a lifting system (105) comprises one or more hydraulic actuators (150) with vertical axis. The hydraulic actuator (150) comprises a cylinder (151) connected to the frame (20) of the base of the vehicle and a piston (152) that slides in the cylinder. The piston (152) is connected to a toothed wheel (153) by means of a pin that lets the toothed wheel (153) rotate around its axis.
The toothed wheel (153) engages in a chain (154). The chain (154) has a first end (154a) fixed to the frame (20) of the vehicle and a second free end (154b). The counterweight (4) is fixed to the second end (154b) of the chain. When the actuator (150) is actuated, the toothed wheel (153) rotates, pulling the chain (154) that lifts the counterweight (4).
In order to let the counterweight (4) rise, the fastenings (22) are directed in vertical direction, as shown in FIG. 5. When the counterweight (4) is in the correct position, the fastenings (22) must be rotated by 90° and directed in horizontal direction in such a way that the counterweight (4) can be positioned on the fastenings (22). Then, the fixing screws (40) are inserted in the counterweight and screwed in the threaded holes of the back wall (21) of the base. With this system, after lifting the counterweight, an operator needs to direct the fastenings (22) in the correct direction while the counterweight is lifted. This is a potentially dangerous operation.
Moreover, this mounting system with actuator (150) and chains (154) needs a counterweight provided with a space to house the actuator (150) when the counterweight is mounted on the base (2).
FIGS. 7 and 8 show an excavator (200) provided with a second type of lifting system (205), which consists in an articulated hydraulic system suitable for mounting and dismounting the counterweight. Such a lifting system (205) uses a special counterweight (204) connected to an articulated arm (250). The articulated arm (250) is connected to the frame (20) of the base of the vehicle in an articulated way. The articulated arm (250) is lifted by a hydraulic cylinder (251).
The articulated arm (250) is connected to the counterweight (204) by means of connecting rods or bars (252). In case of systems with supporting shelves or brackets, after lifting the counterweight (204), the counterweight (204) needs to be centered with respect to the brackets, when the counterweight is in a dangerous condition, meaning that the counterweight is not supported by the brackets of the frame and is not fixed to the brackets with screws.
The counterweight lifting systems of this type, which are currently available on the market, require to modify both the vehicle and the counterweight, the latter having to be suitable for housing the connecting rods (252) and/or the articulated arm. In any case, such articulated hydraulic systems are very expensive.
Other variants of the counterweight lifting systems are known, which consist in articulated hydraulic systems, in which, after mounting the counterweight, the counterweight protrudes in upper position with respect to the hood of the vehicle engine. Such a characteristic of the protruding position of the counterweight with respect to the hood is not a problem for excavators, but represents a serious problem for drilling machines.
With reference to FIGS. 9 and 10, a drilling or boring machine (300) comprises a base (2) mounted on moving means (3), such as tracks. A mast (6) is mounted in an articulated way on the base (2) and a counterweight (4) is fixed to the base (2) in rearward position. A slide slides on the mast (6) and transmits torque and thrust to a drilling tool. As it is known, the mast (6) is a very long shaft, with at least triple length than the base (2). In idle or transportation condition (FIG. 9), the mast is disposed horizontally and protrudes from the base (2) in rearward position, being disposed on the counterweight (4). In working condition (FIG. 10) the mast (6) is raised upwards, and disposed practically vertically.
Currently, the drilling machines that use the base of an ordinary excavator as a base are not provided with counterweight mounting systems. Therefore, the counterweight is mounted with the help of another lifting machine, such as for example a crane (400).
However, the following problems are encountered when using either a crane or one of the known counterweight mounting systems as described above:                when a drilling machine (300) is in idle or transportation condition (FIG. 9), the mast (6) protrudes from the base of the machine in rearward position, above the counterweight (4), making it difficult to dismount the counterweight, given the fact that the mast (6) is disposed between the counterweight and the crane. In view of the above, in order to dismount the counterweight (4) easily, it would be necessary to put the machine in working condition, with the mast (6) raised upwards (see FIG. 10). However, in such a working configuration, the center of gravity of the machine is moved forward, thus reducing the stability of the machine.        
In drilling machines for posts, when the drilling machine is in transportation condition, the mast (6) is disposed horizontally on the machine and must be as close as possible to the counterweight (4) in order to reduce the total height of the machine. In fact, any protruding element above the counterweight (4) could increase the total height of the drilling machine.
The use of the counterweight mounting systems of the prior art would require the modification of the counterweight (4) to make space for an articulated arm or for a hydraulic actuator. Such an operation would be rather difficult and expensive, because the counterweight is generally filled with concrete reinforced with metal scrap, and covered with a thin sheet metal with a thickness of a few millimeters.
Other types of counterweight consist in a cast iron block and therefore also this type of counterweight is difficult to modify.
Moreover, either using the crane (400) or a counterweight mounting system of the prior art, the operator is exposed to a potential hazard both when centering the holes of the counterweight and when rotating the threads of the fastenings for the counterweight.
US2002/00625 discloses a counterweight lifting system that comprises two telescopic arms. Each telescopic arm comprises an internal tube that slides inside an external tube by means of an actuator.
The two external tubes are hinged at the base of the machine. The two external tubes are connected by a plate. An actuator actuates on the plate in a way that the external tubes rotate around the hinging axes.
The internal tubes are perfectly straight. The ends of the internal tubes are connected to a shaft with pulleys around which ropes that are fastened to the counterweight slide.
Such a telescopic arm system protrudes in rearward position from the base of the machine. Consequently, the counterweight cannot be a standard counterweight composed of a parallelepiped block, but must be a special counterweight that is frontally provided with a recessed housing to house the telescopic arms. Therefore, the lifting device of US2002/00625 cannot be used with standard counterweights that are not provided with a suitable housing to house the lifting system.
The purpose of the present invention is to eliminate the drawbacks of the prior art by providing a public works vehicle provided with a counterweight lifting system that is effective, reliable, safe, practical, inexpensive, simple to use and install.
Another purpose of the present invention is to provide a public works vehicle provided with a lifting system that is suitable for being applied to a standard counterweight that is normally used in excavators.